As is well known to those versed in the art, pressurized fluid systems are generally provided with suitable relief means, serving among other purposes that of localizing the relief of excess pressure for safety, convenience and obviating or minimizing economic loss. Toward this end, burst discs have been employed in conduits, vessels and other parts of pressure systems, which discs are calibrated for breakage or rupture under a predetermined fluid pressure. While the use of burst discs has proved satisfactory for pressure relief, there has not been found entirely satisfactory means for indicating the existence and location of a ruptured disc, consistent with safety as from electrical hazards, speed and reliability of indication, and economy in manufacture, installation and maintenance.